Transmission Control Systems: Description and Operation
GENERAL DESCRIPTIONThe 45RFE/545RFE electronic transmission is a conventional transmission in that it uses hydraulically applied clutches to shift a planetary gear train. However, the electronic control system replaces many of the mechanical and hydraulic components used in conventional transmission valve bodies.
The 45RFE/545RFE electronic transmission is a fully electronically controlled transmission. The Transmission Control Module (TCM) is similar to (but not the same as) the one used in the 41TE and 42LE transmissions, therefore many similarities exist in function and diagnosis.
The 45RFE/545RFE has an overrunning clutch (used in 1st gear), an electronically controlled torque converter clutch, 3 planetary gearsets, and six clutch packs. The clutches are called 2nd Clutch (K), 4th Clutch (4C), Low/Reverse Clutch (LR), Reverse Clutch (RC), Underdrive Clutch (UD), and Overdrive Clutch (OD).
Although the 45RFE is considered a 4 speed transmission, it really has 5 forward gear ratios., the 545RFE is considered a 5 speed transmission, it really has 6 forward gear ratios. 2nd gear (1.67:1) and 2nd prime (1.50:1) gear are so close in ratio that they are not considered to be different gear ratios, although both are used as 2nd gear under certain conditions. During most upshift and downshift maneuvers, 2nd gear will be used. 2nd prime gear is only used for a high speed 4-2 downshift. The 545RFE transmission is essentially a software change to the TCM that allows an additional overdrive ratio of (.667:1). The gear ratio of 4th Prime is achieved by applying the 2°C and OD clutches. The 4th Prime is used above 52 MPH. All gear ratios in the 45RFE/545RFE are achieved by applying two elements (clutches). During a shift, one element is released and another is applied, resulting in a different ratio. This is called a clutch to clutch shift. In order to perform a 4-2 downshift, two elements would have to be released and two different elements applied. The 2nd prime gear ratio allows a clutch to clutch 4-2 (2nd prime) downshift.
The oil pump in the 45RFE/545RFE is a dual stage positive displacement gear type pump. At idle and low engine speeds, both stages are working. Once the engine speed reaches a point where one side of the pump can supply the necessary system requirements, the second stage is vented. This pump configuration gives the pressure and flow of a large displacement pump at low speeds, and the economy of a small displacement pump at higher engine speeds. The oil pump housing also contains some of the valves that are found in the valve body in a 41TE or 42LE transmission. The Converter Clutch Switch Valve, Converter Clutch Regulator Valve, Torque Converter Limit Valve, and the Pressure Regulator Valve, are all found in the oil pump housing.
The electronic control system consists of a Transmission Control Module (TCM), a Transmission Range Sensor (TRS), an Input Speed Sensor (ISS), an Output Speed Sensor (OSS), a Line Pressure Sensor (LPS), a Transmission Temperature Sensor (TTS), five pressure switches, and seven solenoids. Each clutch pack has a corresponding solenoid and pressure switch except for the reverse clutch which is controlled by the manual valve. The other two solenoids are called the Multi Select (MS) solenoid and the Pressure Control Solenoid (PCS).
The PCS is used to control line pressure. The 45RFE/54RFE controls line pressure based on inputs to the TCM. The line pressure is torque based (line pressure increases with torque) most of the time, however it is set to a predetermined value just prior to a shift and reverts back to torque based after the shift.
The MS solenoid is used to control the LR clutch during P-R and N-R garage shifts and to control the OD clutch when the Manual Valve is in the "D" position as reported by the TRS. If the manual valve is slightly out of position, the TRS will indicate a temporary zone (T3 or T4). In this case the OD clutch will be controlled by the OD solenoid. Note that if the TRS indicates a temporary zone, this is a valid PRNDL code and will not set a DTC P0706(28). If the PRNDL code consistently indicates a temporary zone while the shift lever is in the "D" position, this would indicate some sort of mechanical problem in the shift linkage as opposed to an electrical TRS problem. Note: vehicle operation in the T3 temporary zone can set a DTC P1715(65).
The 243 Electronic Transfer Case is a conventional transfer case that uses a shift motor to place the transfer case into the desired range. A multiposition switch selector is located on the dash panel in place of a manual shift lever located on the floor.
The Transfer Case shift motor is a bi-directional, 2-wire motor. When the motor is energized, one of the leads is 12volts and the other is ground. Reversing the polarity of the motor changes the direction of the rotation of the motor. The motor has a low speed, high torque output.
The Transfer Case Mode Sensor consists of a magnetic ring and four Hall Effect transistors that convert the shaft position into a coded signal sent to the TCCM. The magnet forces the output of the Hall device low when it is passed over it. The Mode Sensor is supplied 5 volts and a ground from the TCCM and has four output lines that feed back to the TCCM.
The Transfer Case Selector Switch is a multiposition, multi resistance switch that tells the TCCM what range is commanded. The switch assembly also contains a separate Neutral Button and four indicators, one for each selectable range.
FUNCTIONAL OPERATION
The 45RFE/545RFE electronic transmission has a fully adaptive control system. The system performs its functions based on continuous real-time sensor feedback information. The control system automatically adapts to changes in engine performance and friction element variations to provide consistent shift quality. The control system ensures that clutch operation during upshifting and downshifting is more responsive without increased harshness.
The Transmission Control Module (TCM) continuously checks for electrical problems, mechanical problems, and some hydraulic problems. When a problem is sensed, the TCM stores a diagnostic trouble code (DTC). Some of these codes cause the transmission to go into "limp-in" or "default" mode. The 45RFE/545RFE has three default modes:
(I) Immediate shutdown - The TCM deenergizes the transmission control relay. This causes the transmission system to immediately default to third gear if shift lever is in the "D" position, or 2nd gear if it is in the "2" or "L" positions. Park, Neutral, and Reverse are still available.
(0) Orderly Shutdown - If the TCM recognizes a problem that does not require an immediate shutdown, the transmission will maintain the current gear and the transmission control relay will remain energized until deenergizing it will not overspeed the engine. When the vehicle speed reaches a reasonable level the TCM deenergizes the transmission control relay. This causes the transmission system to immediately default to third gear if shift lever is in the "D" position, or 2nd gear if it is in the "2" or "L" positions. Park, Neutral, and Reverse are still available.
(L) Logical Shutdown with Recovery - The TCM does not de-energize the Transmission Control Relay. Instead, the transmission will utilize 1st and 3rd gears while in "D", and will use 2nd while in "2" or "L". All transmission operation in this mode will be at a preset line pressure (open loop). The transmission will resume normal operation (recover) if the detected problem goes away. Three recoveries are permitted in a given key, after the fourth occurrence the operation described above will be maintained.
Once the DRBIII (R) is in the "EATX" portion of the diagnostic program, it constantly monitors the TCM to see if the system is in limp-in mode. If the transmission is in limp-in mode, the DRBIII (R) will flash the red LED.
TRANSMISSION OPERATION AND SHIFT SCHEDULING AT VARIOUS OIL TEMPERATURES
The transmission covered in this manual has unique shift schedules depending on the temperature of the transmission oil. The shift schedule is modified to extend the life of the transmission while operating under extreme conditions.
The oil temperature is measured with a Temperature Sensor on the 45RFE/545RFE transmission. The Temperature Sensor is an integral component of the Transmission Range Sensor (TRS). If the Temperature Sensor is faulty, (DTC P-1799) the transmission will default to a "calculated" oil temperature. Oil temperature will then be calculated using engine coolant temperature, battery/ambient temperature, and engine off time from the Body Control Module (BCM). These inputs are received from the communication bus periodically and are used to initialize the oil temperature at start up. Once the engine is started, the TCM updates the transmission oil temperature based on torque converter slip speed, vehicle speed, gear, and engine coolant temperature to determine an estimated oil temperature during vehicle operation. Vehicles using "calculated oil temperature" track oil temperature reasonably accurately during normal operation. However, if a transmission is overfilled, a transmission oil cooler becomes restricted, or if a customer drives aggressively in low gear, the calculated oil temperature will be inaccurate. Consequently the shift schedule selected may be inappropriate for the current conditions. The key highlights of the various shift schedules are as follows:
Extreme Cold: Oil temperature below -27°C (-16°F) Goes to "Super Cold" schedule when temp rises above -24°C (-12°F) oil temperature Park, Reverse, Neutral and 1st and 3rd gear only No Torque Converter Clutch engagement
Super Cold: Oil temperature between -27°C (-16°F) and -17°C 0°F) Goes to "Cold" schedule above -12°C (10°F) oil temperature
Delayed 2-3 upshift
Delayed 3-4 upshift
Early 4-3 coastdown shift
Early 3-2 coastdown shift
No 3-1 coastdown or kickdown
High speed 4-2, 3-2, 2-1 kickdown shifts are prevented
No Torque Converter Clutch engagement
Cold: Oil temperature between -17°C (0°F) and 2°C (36°F) Goes to "Warm" schedule when temp rises above 4.4°C (40°F) oil temperature
Shifts at higher throttle openings will be early
High speed 4-2, 3-2, 2-1 kickdown shifts are prevented
Delayed 3-4 upshift
Early 4-3 coastdown shift
Torque Converter Clutch engagement allowed with sump temp greater than 18°C (65°F)
Warm: Oil temperature between 2°C (36°F) and 27°C (80°F) Normal operation (upshifts, kickdowns, and coastdowns)
No Torque Converter Clutch engagement
Hot (Normal operation): Oil temperature between 27°C (80°F) and 115°C (240°F) Goes to "Overheat" schedule above 115°C (240°F) oil temperature
Reverts to "Hot" when temp falls below 110°C (230°F)
Normal operation (upshifts, kickdowns, and coastdowns)
Normal Torque Converter Clutch engagement operation
Overheat: Oil temperature above 115°C (240°F) or engine coolant temperature above 118°C (244°F) Reverts to "Hot" when temp falls below 110°C (230°F) oil temp or "Overheat" above 115°C (240°F) oil temp.
Delayed 2-3 upshift 40-51 km/h (25-32 MPH) Delayed 3-4 upshift 66-77 km/h (41-48 MPH) 3rd gear FEMCC from 4877 km/h (30-48 MPH) 3rd gear PEMCC from 43-50 km/h (27-31 MPH) A DTC P0218 High Temperature Operation Activated will be set in the TCM.
Causes for operation in the wrong temperature shift schedule:
Extreme Cold or Cold shift schedule at start up:
Temperature Sensor or circuitry.
Overheat shift schedule after extended operation:
Operation in city traffic or stop and go traffic
Engine idle speed too high - Stuck AIS motor
Aggressive driving in low gear
Long idle time in drive position
Trailer towing in OD gear position (use "2" position if frequent shifting occurs)
Cooling system failure causing engine to operate over 110°C (230°F)
Engine coolant temperature stays low too long - If engine coolant temperature drops below 66°C (150°F) , the transmission will disengage EMCC. Extended operation with the EMCC disengaged will cause the transmission to overheat.
Brake switch or circuitry - The TCM disengages the TCC when it receives a signal from the PCM that the brake has been depressed. A problem with the brake switch or circuitry will cause the EMCC to disengage. Extended operation with the EMCC disengaged will cause the transmission to overheat.
Transmission fluid overfilled
Transmission cooler or cooler lines restricted
Engine cooling fan inoperative
Temperature Sensor or circuitry.
LINE PRESSURE CONTROL
Proper control of the transmission line pressure is essential for proper operation. The 45RFE/ 545RFE normally uses closed loop line pressure control, where actual line pressure (reported by the line pressure sensor) is continuously monitored. The TCM determines the desired (target) line pressure which is required, and adjusts the Pressure Control Solenoid (PCS) until the actual line pressure matches the desired line pressure value. In the event of a line pressure sensor failure DTC P0932(CA), the TCM changes to an open loop control at an essentially constant line pressure.
Proper diagnosis of line pressure systems is facilitated by the use of a special tool (T-fitting - Miller #8259) which allows the use of a mechanical pressure gauge to compare the line pressure sensor reading on the DRBIII (R) to the gauge pressure. Technicians should compare the mechanical gauge reading with the "actual" and "desired" line pressure reading on the DRBIII (R) All three readings should closely match in pressure. Because the mechanical and actual line pressure may not match the desired at low engine speeds (due to low pump output RPM), line pressure should always be checked at 1500 - 2000 RPM.
Typical Line Pressure problems include:
^ Mechanical and "actual" readings both less than desired
- If the mechanical and "actual" readings do not increase significantly as engine speed is raised above 2000 RPM, the pressure control solenoid is usually at fault. The pressure control solenoid is usually accompanied by DTCs P0867(C8) and P0868(C9). The PCS is located in the Transmission Solenoid/TRS assembly.
- If the mechanical and "actual" readings vary with engine speed (above 2000 RPM), the fault is often a sticking main regulator valve. This valve is located in the transmission pump assembly.
^ "Actual" reading on the DRBIII (R) differs from the Mechanical Pressure reading (higher or lower) by more than 69kPa (10 PSI). This is sometimes accompanied by a DTC P0869(CB). The fault is usually in the Line Pressure Sensor or the Line Pressure Sensor Wiring.
^ All three readings match, but the "actual" reading exhibits momentary intermittent pressure increases to 1724 kPa (250 PSI). The line Pressure Sensor is usually the problem. This will cause erratic shift quality (particularly a harsh 3-1 coast down shift), repair by replacing the Line Pressure Sensor.
DRIVE LEARN PROCEDURE
Procedure To Learn A Smooth 1st Neutral To Drive Shift:
Perform this procedure only if the complaint is for a delayed or harsh shift the first time the transmission is put into gear after the vehicle is allowed to set with the engine not running for at least 10 minutes. Use the following steps to have the TCM learn the 1st N-1 UD CVI.
NOTE: The transmission oil temperature must be between 80 - 110°F (27 - 43°C).
1. Start the engine only when the engine and ignition have been off for at least ten (10) minutes.
2. With the vehicle at a stop and the service brake applied, record the UD CVI while performing a Neutral to Drive shift. During the shift, the UD CVI will temporarily show a different value which is the 1st N-1 UD CVI. The 1st N1 UD CVI account for air entrapment in the UD clutch that may occur after the engine has been off for a period of time.
3. Repeat steps 1 and 2 until the recorded 1st N-1 UD CVI value stabilizes.
NOTE: It is important that this procedure be performed when the transmission temperature is between 80 - 11 0F (27 - 43C). If this procedure takes too long to complete fully for the allowed transmission oil temperature, the vehicle may be returned to the customer with an explanation that the shift will improve daily during normal vehicle usage. The TCM also learns at higher oil temperatures, but these values (line pressure correction values) are not available for viewing on the DRBIII (R).
Procedure To Learn A Smooth Neutral To Drive Garage Shift
Perform this procedure if the complaint is for a delayed or harsh shift when the transmission is put into gear after the vehicle has had its first shift. Use the following steps to have the TCM learn the N-1 UD CVI.
NOTE: The transmission oil temperature must be between 80 - 100°F (27 - 43°C) to learn the UD CVI. Additional learning occurs at temperatures as low as 0°F and as high as 200F This procedure may be performed at any temperature that experiences poor shift quality. Although the UD CVI may not change, shift quality should improve.
1. Start the vehicle engine and shift to drive.
2. Move the vehicle forward to a speed of at least 16 km/h (10 MPH) and come to a stop. This ensures no air is present in the UD hydraulic circuit.
3. Perform repeated N-1 shifts at a stop while pausing in Neutral for at least 2-3 seconds and monitor UD CVI volume until the value stabilizes. The value will change during the N-D shift. This is normal since the UD value is different for the N-1 shift then the normal value shown which is used for 4-3 coastdown and kickdowns. Perform repeated shifts in this temperature range until the UD CVI value stabilizes and the N-1 shifts become smooth.
4. This procedure may be performed at any temperature that experiences poor N-1 shift quality. Although the UD CVI may not changes, shift quality should improve.
Procedure To Learn The 1st 2-3 Shift After A Restart Or Shift To Reverse:
Use the following steps to have the TCM learn the 1st 23 shift OD CVI.
NOTE: The transmission oil temperature must be above 80°F (27°C).
1. With the vehicle engine running, select reverse gear for over 2 seconds.
2. Shift the transmission to Drive and accelerate the vehicle from a stop at a steady 15 degree throttle opening and perform a 2-3 shift while noting the OD CVI. During the shift, a different value may appear on the screen, which is the 1st 2-3 OD CVI.
3. Repeat steps 1 and 2 until the 1st 2-3 upshift becomes smooth and the 1st 2-3 OD CVI stabilizes.
Procedure To Learn A Smooth 2-3 And 3-4 Upshift:
Use the following steps to have the TCM learn the OD and 4C CVI's.
NOTE: The transmission oil temperature must be above 110°F (43°C).
1. Accelerate the vehicle from a stop at a steady 15 degree throttle opening and perform multiple 1-2, 2-3, and 3-4 upshifts. The 2nd 2-3 shift following a restart or shift to reverse will be shown during the shift as a value between the 1st 2-3 OD CVI and the normal OD CVI. Updates to the normal OD CVI will occur after the 2nd shift into 3rd gear, following a restart or shift to reverse.
2. Repeat step 1 until the 2-3 and 3-4 shifts become smooth and the OD and 4C CVI become stable.
Procedure To Learn A Smooth 4-3 Coast down And Part Throttle 4-3 Kickdown:
Use the following steps to have the TCM learn the UD shift volume.
NOTE: The transmission oil temperature must be above 110°F (43°C).
1. At a vehicle speed between 64 - 97 Km/H (40 - 60 MPH), perform repeated 4-3 kickdown shifts.
2. Repeat step 1 until the UD volume becomes somewhat stable and the shift becomes smooth.
Procedure To Learn A Smooth 1-2 Upshift and 3-2 Kickdown:
Use the following steps to have the TCM learn the 2C shift volume.
NOTE: The transmission oil temperature must be above 110°F (43°C).
1. With a vehicle speed below 48 Km/H (30 MPH) and the transmission in 3rd gear, perform multiple 3-2 kickdowns.
2. Repeat step 1 until the 3-2 kickdowns become smooth and the 2C CVI becomes stable.
Procedure To Learn A Smooth Manual 2-1 Pulldown Shift As Well As A Neutral To Reverse Shift: Use the following steps to have the TCM learn the LR volume.
NOTE: The transmission oil temperature must be above 110F 43C).
1. With the vehicle speed around 40 - 48 Km/H (25 - 30 MPH) in Manual 2nd, perform manual pulldowns to Low or 1st gear at closed throttle.
2. Repeat step 1 until the LR CVI become stable and the manual 2-1 becomes smooth.
Procedure To Learn A Smooth Neutral To Reverse Shift:
Perform the following shifts.
NOTE: The transmission oil temperature must be above 11 0F 43C).
1. With the vehicle at a stop, perform Neutral to Reverse shifts until the shift is smooth. An unlearned Neutral to Reverse shift may be harsh or exhibit a double bump. If any of the shifts are still not smooth after the clutch volume stabilizes, an internal transmission problem may be present.
Procedure To Learn A Smooth 4-5 Upshift for 545RFE:
Use the following steps to have the TCM learn the 2CA CVI.
NOTE: The transmission oil temperature must be above 110°F (43°C).
1. Accelerate the vehicle through 88 Km/H (55mph) at a steady 10-15 degree throttle opening and perform multiple 4-5 upshifts.
2. Repeat step 1 until the 4-5 shift become smooth and the 2C(A) CVI become stable. There is a separate 2C volume used and learned for 4-5 shifts, 2C(A). It is independent of the 2C CVI learned on 3-2 kickdowns.